This proposal outlines five years of continued work on vasopressin pathways originating in the paraventricular nucleus of the hypothalamus and terminating on the pituitary portal plexus in the median eminence (PVN((VP))-ME) and the pituitary-adrenal system. (A) The organization of the PVN will be studied to determine the relative position and morphology of PVN(VP)-ME neurons including dendritic trees and axonal projections by light and electron microscopic immunocytochemistry on vibratome sections. These neurons will be related to VP neurons projecting to other brain sites and posterior pituitary by orthograde and retrograde tracing methods, and to other peptidergic perikarya by simultaneous methods (oxytocin, neurotensin, substance P, enkephalin). (B) The sites and mechanisms of action of glucocorticoids require investigation at several levels: (1) possible trophic effects in ME on VP axons in response to adrenalectomy; (2) the relationship of brain sites which take up radiolabeled corticosterone (CS) to those projecting directly or indirectly to PVN; (3) bilateral implants of CS and lesions in PVN and other steroid sensitive sites to determine feedback areas. (C) The nature of several possible putative neurotransmitters to the PVN(VP)-ME system suggested by retrograde tracing studies will be investigated in terms of source, sites of termination and possible effects on VP secretion into portal blood: monoamines (autoradiography) serotonin and norepinephrine; peptides (immunocytochemistry): vasoactive intestinal polypeptide, neurotensin, and ACTH and B-endorphin. (D) Reciprocal connections between PVN(VP) neurons and those in other brain nuclei which project to it will be investigated by simultaneous immunocytochemical and tracing methods. (E) The source of the large amounts of VP in portal blood (PVA vs. supraoptic, PVN-ME vs. posterior pituitary) will be studied by radioimmunoassay in animals with bilateral lesions in PVN. Portal vs. peripheral VP, ACTH, and CS will also be studied in reference to administration or removal of steroids, brain lesions and neurotransmitters.